The work in progress under this proposal concentrates in two areas: the terminus requirements of DNA polymerase I in the repair synthesis reaction and the role of novel DNA polymerase activity in the replication of DNA in TR revertants of polCts strains. For the former studies we are using a coupled reaction in which DNA synthesis is dependent in repair enzymes to convert a site of damage to a suitable primer terminus. This approach has allowed the definition of an exonuclease III requirement to convert bleomycin-damage DNA to a suitable primer. For our studies on the novel DNA polymerase activity we have isolated spontaneous revertants from a polA-, polB-, polCts strain of E. coli. A high frequency (50%) of such revertants contain an apparently novel DNA polymerase activity. The genetics and function of this polymerase are being pursued.